The present invention is concerned with devices for the continuous reprofiling by grinding of the surface of the head of one or both rails of a railway track, in situ. Several reprofiling installations mounted on or pulled by railway carriages have been proposed to this day, such as those described for example in the patents CH 606 616; CH 626 673; CH 633 336; CH 653 073; CH 654 047; CH 655 528.
All these conventional grinding devices have in common the fact that they include at least one grinding unit, which has means for guiding it along the rail; means for coupling it to a frame of a railway carriage for its pulling along the railway track; means for moving the grinding unit vertically with respect to the frame and for applying the same against the rail to be reprofiled; and members pressing against the rail to define a reference base of a length sufficient for ensuring that the positioning the grinding unit on the rail be substantially independent of the undulations to be eliminated from the rail; a grinding tool; and means for driving this grinding tool in one or several movements relative to the grinding unit and hence to the rail to be reprofiled.
These installations for reprofiling a rail by grinding differ, on the one hand, by the practical realization of the means and members cited above that they carry and, on the other hand, by the grinding means they use, which can be abrasive shoes, lapping grinders, peripheral grinders or cutters.
The most serious drawback of these known devices, in particular those using rotatory tools such as grinders, resides in the fact that the accuracy of the reprofiling is not sufficient, in particular for the rails used by high speed trains.
FIGS. 1 to 3 and 4 to 6 illustrate schematically the influence of the slack in the bearings of the motor driving the peripheral grinder or the lapping grinder on the quality of fine reprofiling. This slack in the bearings of the driving shaft of the grinder causes oscillations thereof which produce micro-undulations on the head of the reprofiled rail (FIGS. 3 and 6).
One can show that, for oscillations of the grinding axis in the order of 0.25 mm, the undulations or micro-undulations produced on the tread of the rail can exhibit a depth in the order of 0.1 mm and a length between 18 and 20 mm.
These micro-undulations cause annoyance by the noise they produce during the passage of trains, at a frequency in the order of 1200 Hz for trains running at 100 km/hr, and which can extend beyond 3000 Hz for trains running at 250 km/hr.
This phenomenon of creations of micro-undulations on the tread of the head of the rail occurs in all cases, whatever the device used for reprofiling using a rotatory tool in contact with the rail, may it be a grinder or a cutter. These deformations of the rail are clearly illustrated in the plan view of FIGS. 2 and 5 and in the longitudinal cross-sectional view of FIGS. 3 and 6.
One can see that this phenomenon of creation of micro-undulations along the surface of the rail occurs when the reprofiling thereof is carried out by means of shoes or scrapers in contact with the rail.
At the present time, the reprofiling of the rail by means of abrasive shoes subjected to a continuous or an alternating motion in the direction of the longitudinal axis of the rail is completely abandoned because the abrading capacity, i.e. of the capacity of these shoes to remove the metal, is totally insufficient and the rail cannot be used by trains for an excessive duration of time.
The use of an abrasive web for the reprofiling of the rails has also been proposed, but these attempts have not been satisfactory. Patent CH 356 483 describes a reprofiling device in which an abrasive web is held taught under a shoe provided with running rollers at its ends. The abrasive web is fixed, the portion in contact with the rail can be replaced by a new portion manually when worn. Patent EP 0 512 159 describes a device for grinding the rail including a continuous abrasive web, held around rollers, of which three are in contact with the rail. These two devices in CH 356 483 and EP 0 512 159 have the same drawback as the devices discussed previously, since they include wheels or rollers applying the abrasive web against the rail, and accordingly these rollers exhibit necessarily some slack and this produces necessarily micro-undulations on the surface of the rail.
Patent EP 0 371 328 describes a device for grinding a rail by means of a continuous abrasive web, closed on itself and driven by this motor. This abrasive web moves along a plane perpendicular to the longitudinal axis of the rail, which necessitates the use of lower rollers on which passes the abrasive web which are placed laterally with respect to the rail and slightly lower that the rail tread. This is a serious drawback since such a device cannot be pulled along the railway track without having to be frequently lifted to avoid the obstacles found along the rail.
Thus, no solution proposed at this time for the reprofiling and the grinding of the rail has been capable of avoiding the creation or of eliminating the micro-undulations formed along the tread surface and which can induce unacceptable noise levels, when a train travels at high speed.